Radar, or radio detection and ranging, typically involves the transmission of electromagnetic energy through the atmosphere to an area of interest. The electromagnetic energy is reflected by objects in the area of interest and the reflections are analyzed to determine the objects' range and direction.
Two parameters of a radar system's performance that are of particular interest are the maximum range at which objects can be detected and the resolution with which they can be located and tracked, once detected. Often, however, one characteristic is enhanced at the expense of the other. For example, systems employing an approach known as over-the-horizon radar (OTHR) can detect objects over long ranges but with only poor azimuth resolution. This is due to their long wavelength and limited antenna size. Alternatively, a technique referred to as synthetic aperture radar (SAR) typically provides good azimuth resolution but, to date, has been applied only to microwave systems where line-of-sight propagation occurs.